1. Field of the Invention
The present invention relates to a method of producing a golf ball, capable of forming a cover to have a uniform thickness to produce a golf ball excellent in resistance to chunking (resistance to abrasion).
2. Description of the Conventional Art
Conventionally in producing a golf ball, an injection molding process or a heat and compression molding process is generally employed to place a cover on a core. As an example of the injection molding process, U.S. Publication No. U.S. Ser. No. 2003/0064832A1 discloses a method to inject a previously prepared material for a cover to be molded around a core for coverage. In the injection molding process, however, at an initial stage of injection of a material for a cover, a core is held by a pin at a center of a cavity, and when the injection enters a final stage, the pin recedes. As such the injection molding process can result in the core having its center offset from the ball's center and tend to provide a cover having an uneven thickness. A golf ball having a cover of a large thickness (for example of 1.4 to 2.3 mm) often ensures that it has sufficient physical properties even if injection molding provides a cover having an uneven thickness. If a cover has a small thickness (for example of 0.3 to 1.0 mm), however, and the thickness is uneven, it significantly negatively affects the ball's performance. Injection molding has its limit when it is used as described above.
By contrast, the heat and compression molding process, as compared with the injection molding process, can form a cover to have a uniform thickness. Accordingly for a cover having a small thickness, the heat and compression molding process can suitably be employed. U.S. Publication No. U.S. 2003/0064828A1 describes that in producing a solid golf ball including a cover having a thickness of 0.5 to 2.0 mm the cover's material or two half shells are compression molded to cover an intermediate layer. When a cover has a small thickness, however, the heat and compression molding process cannot provide the cover with a uniform thickness, facilitating the cover to partially have an insufficient thickness, an uneven thickness, or the like. Further, the cover's physical properties, resistance to abrasion in particular, cannot sufficiently be acquired just by controlling a covering process so as to provide a cover with a uniform thickness.